fix(sdk-android): post frame callbacks via main looper

Choreographer.getInstance() is per-thread and throws on threads
without a Looper. The previous impl called it from the SocketClient
reader thread, which surfaced as snapshot failures with empty
state during the sample-app round trip. Now the reader thread
posts a Runnable to the main Handler that, on the main thread,
gets the Choreographer and posts the frame callback.

sdk/android/src/main/kotlin/dev/uatu/sdk/ChoreographerPoster.kt

@@ -1,9 +1,15 @@
 package dev.uatu.sdk
 
+import android.os.Handler
+import android.os.Looper
 import android.view.Choreographer
 
 class ChoreographerPoster : FrameCallbackPoster {
+    private val mainHandler = Handler(Looper.getMainLooper())
+
     override fun postFrameCallback(callback: () -> Unit) {
+        mainHandler.post {
             Choreographer.getInstance().postFrameCallback { callback() }
         }
     }
+}